The present invention relates to an electromagnetic actuator that generates a driving force by an electromagnetic force. More specifically, the present invention relates to an electromagnetic actuator that generates a rotational driving force by rotating by a predetermined angle range and that is employed for driving a camera shutter or the like, and the present invention relates to a camera shutter unit using this electromagnetic actuator.
A conventional electromagnetic actuator is made up of, for example, a rotor magnetized with different polarities (the N pole and the S pole), a pair of arcuate magnetic pole parts disposed in such a way as to surround a part of the outer circumferential surface of the rotor, a yoke (magnetic-path forming member) that magnetically connects the magnetic pole parts to each other and forms a magnetic path (magnetic circuit), a magnetizing coil wrapped around a part of the yoke, etc.
However, since this structure has a disadvantage in the fact that a magnetic attraction force by which the rotor is maintained at an initial position (resting position) is weak in a current-stopped state in which an electric current is not passed through the coil, a technique is employed in which, for example, the relationship between the pair of magnetic pole parts and the magnetization angle of the rotor is changed, or a magnetic gap between the outer circumferential surface of the rotor and the magnetic pole parts is narrowed, in order to strengthen the magnetic attraction force and raise the maintaining force. Without being limited to the situation of the initial position (resting position), this technique is likewise applied to a situation in which the rotor is maintained at the maximum rotational position where the rotor has rotated angularly to the maximum.
In order to raise the maintaining force according to techniques like the aforementioned one, there arises a need to set an actuating voltage (lowest actuating voltage) required to actuate the rotor at a high level in any technique, thus bringing about an increase in power consumption. On the other hand, in order to set the lowest actuating voltage at a low level, there is a technique of, for example, extending an area where the outer circumferential surface of the rotor faces the magnetic pole part. However, if this technique is employed, a magnetic attraction force (rotational urging force) that prompts rotation will be oppositely lowered, thereby bringing about a decrease in the maintaining force serving to urge it in a predetermined rotational direction and maintain it.
As a conventional electromagnetic actuator, one of U.S. Pat. No. 5,689,746 is known. In this electromagnetic actuator, yokes, which form magnetic pole parts and are opposite to each other with a rotor therebetween, branch into two parts to each be linear, and one of them holds a coil. However, if these yokes are disposed around the opening of a camera and are used as driving sources of a shutter unit, a space cannot be efficiently exploited, thus leading to the enlargement of the unit.
The present invention has been made in consideration of the problems of the conventional techniques, and an object of the present invention is to provide an electromagnetic actuator capable of giving a desired rotational urging force to a rotor and maintaining the rotor at a predetermined position, and capable of heightening a driving force when rotated, while aiming for structural simplification or size reduction without raising an actuating voltage, i.e., under the state of controlling power consumption. Another object is to provide a camera shutter unit that employs this electromagnetic actuator.
An electromagnetic actuator according to a first aspect of the present invention includes a magnetizing coil; a rotor that is magnetized with different polarities and rotates by a predetermined angle range between an initial position taken when an electric current is stopped and a maximum rotational position where the rotor rotates angularly to the maximum when an electric current is applied, thereby outputting a driving force; and a first magnetic pole part and a second magnetic pole part that are disposed so as to face an outer circumferential surface of the rotor and that generate mutually different magnetic poles through a magnetic path when an electric current is passed through the coil; in which the rotor has a projection that is magnetized with one of the different polarities and that projects outward in its radial direction, and, in the vicinity of the first magnetic pole part, an auxiliary magnetic pole piece is provided that is disposed so as to be close to or be in contact with the projection when the rotor is located at the initial position and that generates the same magnetic pole as the first magnetic pole part when a current is applied.
According to this structure, when the rotor is located at the initial position in the current-stopped state, a strong magnetic attraction force acts between the projection of the rotor and the auxiliary magnetic pole piece, and the rotor is infallibly maintained at the initial position. On the other hand, in the current-running state, the same magnetic pole as the magnetic pole with which the rotor projection is magnetized occurs in the auxiliary magnetic pole piece, and a strong repulsion force occurs, thereby rotating the rotor swiftly in a predetermined direction.
An electromagnetic actuator according to a second aspect of the present invention includes a magnetizing coil; a rotor that is magnetized with different polarities and rotates by a predetermined angle range between an initial position taken when an electric current is stopped and a maximum rotational position where the rotor rotates angularly to the maximum when an electric current is applied, thereby outputting a driving force; and a first magnetic pole part and a second magnetic pole part that are disposed so as to face an outer circumferential surface of the rotor and that generate mutually different magnetic poles through a magnetic path when an electric current is passed through the coil; in which the rotor has a projection that is magnetized with one of the different polarities and that projects outward in its radial direction, and, in the vicinity of the first magnetic pole part, a first auxiliary magnetic pole piece is provided that is disposed so as to be close to or be in contact with the projection when the rotor is located at the initial position and that generates the same magnetic pole as the first magnetic pole part when a current is applied, and, in the vicinity of the second magnetic pole part, a second auxiliary magnetic pole piece is provided that is disposed so as to be close to or be in contact with the projection when the rotor is located at the maximum rotational position and that generates the same magnetic pole as the second magnetic pole part when a current is applied.
According to this structure, in addition to the same action as the aforementioned one, when the rotor is located at the maximum rotational position, a strong magnetic attraction force acts between the projection and the second auxiliary magnetic pole piece, and the rotor is infallibly maintained at the maximum rotational position. On the other hand, when a current is applied in an opposite direction in this state, the same magnetic pole as the magnetic pole with which the rotor projection is magnetized occurs in the second auxiliary magnetic pole piece, and a strong repulsion force occurs, thereby rotating the rotor swiftly in the opposite direction and returning it to the initial position.
In the aforementioned structure, the auxiliary magnetic pole piece may be formed by bending a planar magnetic member so as to be close to or be in contact with the projection.
According to this structure, the auxiliary magnetic pole piece can be formed to have a wide area while aiming for structural simplification and weight reduction, and a magnetic attraction force or repulsion force acting between the projection and the auxiliary magnetic pole piece can be efficiently generated.
In the aforementioned structure, the rotor may have an output pin, which has been integrally formed, for outputting its rotational driving force, and the output pin may be used also as the projection. According to this structure, there is no need to form another projection, and the rotor can be structurally simplified, or a conventional molding method can be reused.
In the aforementioned structure, the first magnetic pole part and the second magnetic pole part may be positioned at both ends, respectively, of a magnetic-path forming member that has a part around which a coil is wrapped and that forms a magnetic path. The auxiliary magnetic pole piece may branch from a part that forms the first magnetic pole part, and the coil may be wrapped around two places of the magnetic-path forming member. According to this structure, the magnetic operation force can be heightened while aiming for structural simplification.
In the aforementioned structure, the first magnetic pole part and the second magnetic pole part may be positioned at both ends, respectively, of a magnetic-path forming member that has a part around which a coil is wrapped and that forms a magnetic path. The first auxiliary magnetic pole piece may branch from a part that forms the first magnetic pole part, and the second auxiliary magnetic pole piece may branch from a part that forms the second magnetic pole part, and the coil may be wrapped around two places of the magnetic-path forming member. According to this structure, likewise, the magnetic operation force can be heightened while aiming for structural simplification.
In the aforementioned structure, the first magnetic pole part and the second magnetic pole part may be disposed so as to generate a magnetic urging force by which the rotor is returned to the initial position when no current is passed through the coil. According to this structure, when a current-stopped state is reached, the rotor always returns to the initial position independently of the rotational position (e.g., maximum rotational position) of the rotor.
In the aforementioned structure, the first magnetic pole part and the second magnetic pole part may be disposed so as to generate a magnetic urging force by which the rotor is maintained at the maximum rotational position when the application of a current to the coil is stopped in a state in which the rotor is located at the maximum rotational position. According to this structure, the rotor is infallibly maintained at the maximum rotational position in spite of the fact that no current is applied under the state in which the rotor has reached the maximum rotational position.
An electromagnetic actuator according to a third aspect of the present invention includes a magnetizing coil; a rotor that has a first outer circumferential surface and a second outer circumferential surface which are magnetized with different polarities and into which the rotor is divided, the rotor rotating by a predetermined angle range between an initial position taken when an electric current is not applied and a maximum rotational position where the rotor rotates angularly to the maximum when an electric current is applied, thereby outputting a driving force; and a yoke that has a first magnetic pole part and a second magnetic pole part that are disposed so as to face an outer circumferential surface of the rotor and that generate mutually different magnetic poles when an electric current is passed through the coil; in which the rotor has a projection that is magnetized with one of the different polarities and that projects outward in its radial direction, and, in the vicinity of the first magnetic pole part, an auxiliary magnetic pole piece is provided that is disposed so as to be close to or be in contact with the projection when the rotor is located at the initial position and that generates the same magnetic pole as the first magnetic pole part when a current is applied, and the first magnetic pole part has a first wide facing surface that faces the first outer circumferential surface of the rotor over a length wider than a predetermined one in a rotational direction of the rotor, and the second magnetic pole part has a second wide facing surface that faces the second outer circumferential surface of the rotor over a length wider than a predetermined one in the rotational direction of the rotor.
According to this structure, when the rotor is located at the initial position in the current-stopped state, a magnetic attraction force acts between the rotor projection and the auxiliary magnetic pole piece, and the rotor is infallibly maintained at the initial position. On the other hand, in the current-running state, a repulsion force resulting from the fact that the same magnetic pole as a magnetic pole with which the rotor projection is magnetized has occurred is generated in the auxiliary magnetic pole piece, and a strong repulsion force is generated also between the first wide facing surface and the first outer circumferential surface and between the second wide facing surface and the second outer circumferential surface, thus giving a strong rotational force to the rotor and rotating the rotor swiftly in the predetermined direction.
In the aforementioned structure, the yoke may be made up of a first planar yoke and a second planar yoke that are laid on each other in the direction of a rotational shaft of the rotor, the first yoke provided with the first wide facing surface, the second wide facing surface, and the auxiliary magnetic pole piece, and the second yoke provided with the first wide facing surface and the second wide facing surface.
According to this structure, it is possible to easily form the first wide facing surface and the auxiliary magnetic pole piece that constitute the first magnetic pole part, the second wide facing surface that constitutes the second magnetic pole part, etc., and to achieve structural simplification.
An electromagnetic actuator according to a fourth aspect of the present invention includes a magnetizing coil; a rotor that has a first outer circumferential surface and a second outer circumferential surface which are magnetized with different polarities and into which the rotor is divided, the rotor rotating by a predetermined angle range between an initial position taken when an electric current is not applied and a maximum rotational position where the rotor rotates angularly to the maximum when an electric current is applied, thereby outputting a driving force; and a yoke that has a first magnetic pole part and a second magnetic pole part that are disposed so as to face the outer circumferential surface of the rotor and that generate mutually different magnetic poles when an electric current is passed through the coil; in which the rotor has a projection that is magnetized with one of the different polarities and that projects outward in its radial direction, and, in the vicinity of the first magnetic pole part, an auxiliary magnetic pole piece is provided that is disposed so as to be close to or be in contact with the projection when the rotor is located at the initial position and that generates the same magnetic pole as the first magnetic pole part when a current is applied, and the first magnetic pole part has a first wide facing surface that faces the first outer circumferential surface of the rotor over a length wider than a predetermined one in a rotational direction of the rotor and has a first narrow facing surface narrower than the first wide facing surface that faces the first outer circumferential surface of the rotor, and the second magnetic pole part has a second wide facing surface that faces the second outer circumferential surface of the rotor over a length wider than a predetermined one in the rotational direction of the rotor and has a second narrow facing surface narrower than the second wide facing surface that faces the second outer circumferential surface of the rotor.
According to this structure, when the rotor is located at the initial position in the current-stopped state, a strong magnetic attraction force (rotational urging force) acts between the rotor projection and the auxiliary magnetic pole piece, between the first narrow facing surface and the first outer circumferential surface, and between the second narrow facing surface and the second outer circumferential surface by appropriately selecting the positions where the first narrow facing surface and the second narrow facing surface are disposed, and therefore the rotor is infallibly maintained at the initial position. On the other hand, in the current-running state, a repulsion force resulting from the fact that the same magnetic pole as a magnetic pole with which the rotor projection is magnetized has occurred is generated in the auxiliary magnetic pole piece, and a strong repulsion force is generated also between the first wide facing surface and the first outer circumferential surface and between the second wide facing surface and the second outer circumferential surface, thus giving a strong rotational force to the rotor and rotating the rotor swiftly in the predetermined direction.
In the aforementioned structure, the yoke may be made up of a first planar yoke and a second planar yoke that are laid on each other in the direction of a rotational shaft of the rotor, the first yoke provided with the first narrow facing surface, the second narrow facing surface, and the auxiliary magnetic pole piece, and the second yoke provided with the first wide facing surface and the second wide facing surface.
According to this structure, it is possible to easily form or select surfaces and pieces different in width, such as the first wide facing surface, the first narrow facing surface, and the auxiliary magnetic pole piece that constitute the first magnetic pole part, and the second wide facing surface and the second narrow facing surface that constitute the second magnetic pole part. Further, it is possible to achieve structural simplification.
An electromagnetic actuator according to a fifth aspect of the present invention includes a magnetizing coil; a rotor that has a first outer circumferential surface and a second outer circumferential surface which are magnetized with different polarities and into which the rotor is divided, the rotor rotating by a predetermined angle range between an initial position taken when an electric current is not applied and a maximum rotational position where the rotor rotates angularly to the maximum when an electric current is applied, thereby outputting a driving force; and a yoke that has a first magnetic pole part and a second magnetic pole part that are disposed so as to face the outer circumferential surface of the rotor and that generate mutually different magnetic poles when an electric current is passed through the coil; in which the rotor has a projection that is magnetized with one of the different polarities and that projects outward in its radial direction, and, in the vicinity of the first magnetic pole part, an auxiliary magnetic pole piece is provided that is disposed so as to be close to or be in contact with the projection when the rotor is located at the initial position and that generates the same magnetic pole as the first magnetic pole part when a current is applied, and the first magnetic pole part has a first wide facing surface that faces the first outer circumferential surface of the rotor over a length wider than a predetermined one in a rotational direction of the rotor and has a first narrow facing surface narrower than the first wide facing surface that faces the first outer circumferential surface of the rotor, and the second magnetic pole part has a second narrow facing surface that faces the second outer circumferential surface of the rotor over a narrow length less than a predetermined one in the rotational direction of the rotor.
According to this structure, when the rotor is located at the initial position in the current-stopped state, a strong magnetic attraction force (rotational urging force) acts between the rotor projection and the auxiliary magnetic pole piece, between the first narrow facing surface and the first outer circumferential surface, and between the second narrow facing surface and the second outer circumferential surface by appropriately selecting the positions where the first narrow facing surface and the second narrow facing surface are disposed, and therefore the rotor is infallibly maintained at the initial position. On the other hand, in the current-running state, a strong repulsion force resulting from the fact that the same magnetic pole as a magnetic pole with which the rotor projection is magnetized has occurred is generated in the auxiliary magnetic pole piece, and a repulsion force is generated also between the first wide facing surface and the first outer circumferential surface, thus giving a rotational force to the rotor and rotating the rotor swiftly in the predetermined direction.
In the aforementioned structure, the yoke may be made up of a first planar yoke and a second planar yoke that are laid on each other in the direction of a rotational shaft of the rotor, the first yoke provided with the first narrow facing surface, the second narrow facing surface, and the auxiliary magnetic pole piece, and the second yoke provided with the first wide facing surface and the second narrow facing surface.
According to this structure, it is possible to easily form or select surfaces and pieces different in width, such as the first wide facing surface, the first narrow facing surface, and the auxiliary magnetic pole piece that constitute the first magnetic pole part, and the second narrow facing surface that constitutes the second magnetic pole part. Further, it is possible to achieve structural simplification.
An electromagnetic actuator according to a sixth aspect of the present invention includes a magnetizing coil; a rotor that has a first outer circumferential surface and a second outer circumferential surface which are magnetized with different polarities and into which the rotor is divided, the rotor rotating by a predetermined angle range between an initial position taken when an electric current is not applied and a maximum rotational position where the rotor rotates angularly to the maximum when an electric current is applied, thereby outputting a driving force; and a yoke that has a first magnetic pole part and a second magnetic pole part that are disposed so as to face the outer circumferential surface of the rotor and that generate mutually different magnetic poles when an electric current is passed through the coil; in which the rotor has a projection that is magnetized with one of the different polarities and that projects outward in its radial direction, and, in the vicinity of the first magnetic pole part, an auxiliary magnetic pole piece is provided that is disposed so as to be close to or be in contact with the projection when the rotor is located at the initial position and that generates the same magnetic pole as the first magnetic pole part when a current is applied, and the first magnetic pole part has a first wide facing surface that faces the first outer circumferential surface of the rotor over a length wider than a predetermined one in a rotational direction of the rotor, a first narrow facing surface that is disposed close to the first wide facing surface in the rotational direction of the rotor and that is narrower than the first wide facing surface that faces the first outer circumferential surface of the rotor, and a second narrow facing surface that is disposed close to the first wide facing surface in the direction of a rotational shaft of the rotor and that is narrower than the first wide facing surface in the rotational direction of the rotor that faces the first outer circumferential surface of the rotor; and the second magnetic pole part has a second wide facing surface that faces the second outer circumferential surface of the rotor over a length wider than a predetermined one in the rotational direction of the rotor, and a third narrow facing surface that is disposed close to the second wide facing surface in the rotational direction of the rotor and that is narrower than the second wide facing surface.
According to this structure, when the rotor is located at the initial position in the current-stopped state, a strong magnetic attraction force (rotational urging force) acts between the rotor projection and the auxiliary magnetic pole piece and between the second narrow facing surface and the first outer circumferential surface, by appropriately selecting the positions where the first narrow facing surface, the second narrow facing surface, the third narrow facing surface, etc., are disposed, and therefore the rotor is infallibly maintained at the initial position. On the other hand, in the current-running state, a strong repulsion force resulting from the fact that the same magnetic pole as a magnetic pole with which the rotor projection is magnetized has occurred is generated in the auxiliary magnetic pole piece, and a repulsion force is generated also between the first wide facing surface and the first outer circumferential surface and between the second wide facing surface and the second outer circumferential surface, thus giving a rotational force to the rotor and rotating the rotor swiftly in the predetermined direction.
Further, when a current is applied, for example, in an opposite direction at the maximum rotational position, a strong attraction force is generated between the first narrow facing surface and the first outer circumferential surface and between the third narrow facing surface and the second outer circumferential surface, thus rotating the rotor swiftly toward the initial position.
In the aforementioned structure, the yoke may be made up of a first planar yoke and a second planar yoke that are laid on each other in the direction of the rotational shaft of the rotor, the first yoke provided with the second narrow facing surface, the second wide facing surface, the third narrow facing surface, and the auxiliary magnetic pole piece, and the second yoke provided with the first wide facing surface, the first narrow facing surface, the second wide facing surface, and the third narrow facing surface, in which the first wide facing surface, the second narrow facing surface, and the second wide facing surface are disposed to face each other with the rotor therebetween, and the first narrow facing surface and the third narrow facing surface are disposed to face each other with the rotor therebetween.
According to this structure, it is possible to easily form or select surfaces and pieces different in width, such as the first wide facing surface, the first narrow facing surface, the second narrow facing surface, and the auxiliary magnetic pole piece that constitute the first magnetic pole part, and the second wide facing surface and the third narrow facing surface that constitute the second magnetic pole part. Further, it is possible to achieve structural simplification.
In the electromagnetic actuator of the present invention, the first wide facing surface of the second yoke may be formed by bending a part of the second yoke in the direction of the rotational shaft of the rotor.
According to this structure, the first wide facing surface that faces the first outer circumferential surface of the rotor can be made larger, and, proportionately with it, the rotational force in the current-running state can be raised.
Further, in the electromagnetic actuator of the present invention, the auxiliary magnetic pole piece may be formed by bending a part of the first yoke so as to be close to or be in contact with the projection.
According to this structure, the auxiliary magnetic pole piece can be formed to have a wide area while aiming for structural simplification and weight reduction, and the magnetic attraction force or the repulsion force acting upon the projection can be efficiently generated.
Further, in the electromagnetic actuator of the present invention, the rotor may have an output pin that is integrally formed, and that is used to output its rotational driving force, and that is used also as the projection.
According to this structure, there is no need to independently form another projection, and the rotor can be structurally simplified, or a conventional molding method can be reused.
An electromagnetic actuator according to a seventh aspect of the present invention includes a magnetizing coil; a rotor that is magnetized with different polarities and rotates by a predetermined angle range between an initial position taken when an electric current is not applied and a maximum rotational position where the rotor rotates angularly to the maximum when an electric current is applied, thereby outputting a driving force; and a yoke that has a first magnetic pole part and a second magnetic pole part that are disposed so as to face the outer circumferential surface of the rotor and that generate mutually different magnetic poles when an electric current is passed through the coil; in which the rotor has a projection that is magnetized with one of the different polarities and that projects outward in its radial direction, and, in the vicinity of the first magnetic pole part, an auxiliary magnetic pole piece is provided that is disposed so as to be close to or be in contact with the projection when the rotor is located at the initial position and that generates the same magnetic pole as the first magnetic pole part when a current is applied, and the yoke has a first long part that forms the first magnetic pole part in an end area thereof and a second long part that forms the second magnetic pole part in an end area thereof, the first long part having a bent shape, and the second long part having a linear shape by which the coil is held.
According to this structure, since the coil is held by the second long part having a linear shape, the coil can be easily attached, and, on the other hand, since the first long part has a bent shape, the first long part can be disposed along an opening when it is used as, for example, a driving source for a camera shutter unit, thus allowing the unit to become more compact.
A camera shutter unit according to an eighth aspect of the present invention includes a base plate to define an opening for exposure, a shutter blade mounted on the base plate so that it can freely reciprocate between an open position where the opening is opened and a closed position where the opening is closed, and a driving source to exert a driving force for reciprocating the shutter blade, and the driving source is any one of the aforementioned electromagnetic actuators of the first through seventh aspects of the present invention.
According to this structure, the shutter blade is driven by a desired rotational driving force without raising an actuating voltage, i.e., with low power consumption in the current-running state, whereas the shutter blade is infallibly maintained at a predetermined resting position (initial position) in the current-stopped state.